Soy: East and West

Soy is used medicinally in both the east and the west. Other medicinal plants in this family include red clover, indigo, alfalfa, fenugreek, senna, kudzu, mimosa, and astragalus. Parts of this plant that are used medicinally include the bean, the sprout, and the skin of the bean pod. The most common part used is the bean and it is typically taken as a food, though capsules and decoctions are other ways to benefit from the medicinal actions of this plant. Some of the different ways in which soy can be prepared include edamame (steamed bean pods), tofu (coagulated soymilk), tempeh (fermented soybean cake), miso (fermented soybean paste), natto (fermented soybean condiment), tamari (soybeans fermented in water), and soy sauce (soybeans and wheat fermented in water).


Western herbal medicine uses soybeans for their phytoestrogens and beneficial effects on the heart and circulatory system. Soybeans are rich in estrogenic isoflavones, chemicals that are so similar to human estrogen that our bodies can readily modify them to supplement our hormone levels. This makes soybeans a valuable ally for reducing menopausal symptoms, treating reproductive hormonal imbalances, and preventing osteoporosis. These isoflavones can even reduce the risk of hormone-dependent cancers, like breast and prostate cancer, because they are similar enough to bind human estrogen receptors but different enough that they don't stimulate cancer cells. Soybeans have also been shown to reduce triglyceride and serum cholesterol, especially the harmful low-density lipoproteins, without adversely affecting levels of the beneficial high-density lipoproteins. Because of this, soybeans are commonly taken for heart disease and atherosclerosis (hardening of the arteries).

In the east, soy has a long history as a medicinal herb. There are three different forms in which this plant is used: prepared soybean, soybean sprout, and the skin of the soybean pod. As with other herbs, different parts of the plant have different actions and indications. Take the prepared soybean, for example. This is traditionally made by steaming the beans in a decoction of wormwood and mulberry leaf and then leaving the beans to ferment in the liquid. In this form, soy is used to treat the initial stages of viral infections and the irritability, restlessness, and insomnia that can follow fevers. The sprout, on the other hand, is used for heat-stroke, while the soybean skin is used for dizziness, headaches, and night sweats. Interestingly, all three forms are applicable for different situations in which the body is overheated: the bean for fevers, the sprout for heat-stroke, and the skin for night sweats. What we would say in Chinese medicine, therefore, is that soy is energetically cooling.


As a food, soybeans have certain cautions and contradictions. First, it is the second most allergenic food after peanuts. Second, many people have difficulty digesting soybeans, especially when eaten unfermented, with the most common symptoms being stomachache, constipation, and diarrhea. Third, since soybeans are so high in phytoestrogens, it is necessary to be careful when feeding this plant to developing children, and caution is recommended when utilizing it in baby formulas, especially the soy protein isolate. The high amount of phytoestrogens also means that intensive use by pregnant women can exert hormonal effects on the developing fetus. These phytoestrogens can have anti-thyroid properties as well, so habitual consumption can cause hypothyroidism, low energy, poor mineral absorption, infertility, and may even reduce the absorption of pharmaceutical thyroid medications.

Another important thing to note about soybeans is that, like all beans, they contain phytic acid in their skin, a chemical that prevents them from being digested. Since beans are seeds, this chemical increases the chances that the beans will pass through the digestive tracts of animals whole, distributing them farther afield, both fertilizing the plant with their stool and propagating the species. Unfortunately, phytic acid also binds to minerals in our bodies like calcium, magnesium, and zinc, reducing their absorption. This is bad for small children, who depend on these minerals to build new bone, for those who suffer from osteoporosis, and for malnourished individuals who are already deficient in these minerals. Soybeans also contain an anticoagulant that prevents the breakdown of proteins and vitamin B12, and hemagglutinins that can clump red blood cells together, so they should be used cautiously by people who have conditions like anemia and clotting disorders.

Fortunately, there is a way to deactivate the phytic acid, anti-coagulants, and hemagglutinins in beans. Cooking and sprouting are somewhat successful, but both are only partially effective. As it turns out, the best way to fully deactivate these chemicals is with fermentation. That's right, only bacterial, molds, and yeast have the enzymes necessary to make soy optimally digestible for us! This is why soybeans are traditionally eaten fermented in the east, as tempeh, miso, natto, tamari, and soy sauce, all fermented forms of soy. (Please note that tofu is not a fermented food, so it is not as digestible. Tofu is more like cheese, made by coagulating the proteins out of soybean milk with calcium sulfate or other salts.) So enjoy your soy but keep in mind that it does have effects on our hormones, it is a common allergen, and it is easiest to digest if it is fermented.

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